In communications systems, the term “jitter” refers to a deviation from the expected value of a periodic signal over time. Since some jitter is inevitable, there is a need for modern communications systems to exhibit some tolerance to jitter, and still meet performance requirements. Indeed many industry standards require communications systems to have a minimum tolerance for jitter, which is measured according to various metrics. Manufacturers, researchers, engineers, and end users, therefore, are very concerned with testing the jitter tolerance of communications components and systems.
Traditionally, jitter tolerance has been tested using external test equipment to introduce various types of jitter to the system-under-test. Using the traditional external test equipment, jitter (also called interferers herein) is introduced into the system and the system's tolerance is determined by analyzing the output of the system.
There are multiple problems with external test equipment. First, external test equipment for jitter is very expensive. For example, test equipment for systems with high transmission rates (e.g., 40 gigabits per second) can cost upwards of half a million dollars. Second, tests performed using external equipment are time consuming. Third, a single piece of test equipment cannot be in two places at once, thereby limiting the availability of jitter testing.